During agricultural seeding operations, placing fertilizer in soil at controlled separation from seed helps prevent high fertilizer concentrations from harming the young plants. Machines are available with a machine configuration having separate openers for seed and fertilizer. With many of the separate opener configurations, there is a reduced number of fertilizer openers. Typically there is one fertilizer opener for two seed openers, and the fertilizer application point is approximately equally spaced between the two seed application points. An example of such a machine is the John Deere 1895 Air Drill with two rows of disk-type rockshaft-mounted seed openers combined with one row of disk-type rockshaft-mounted fertilizer openers. Another example is the Bourgault 5710 Air Hoe Drill with shank-type frame-mounted seed openers and frame-mounted disk-type fertilizer openers. Disk-type openers are relatively complex and expensive compared to hoe openers. However, disks tend to have lower draft and higher residue flow capacity. Controlling fertilizer placement depth on frame mounted fertilizer openers can be difficult and time-consuming.
On implements wherein the operating depth of a shank opener is set by the machine frame position, changes in fertilizer placement relative to seed placement require adjustment of the position of a disk-type fertilizer opener relative to the frame. Changes in the disk opener position relative to the frame are also required to raise the disk opener above the ground surface when only the shank openers are in use. Rockshaft mounted openers typically have a limited range of preferred rotational position due to a limited acceptable range of attack angles between the application boot and the soil surface.